A standard six-high rolling stand of the type used for rolling strip steel has a pair of vertically spaced nip-defining working rolls of relatively small diameter. Respective upper and lower inner backup rolls of larger diameter bear respectively down and up toward the nip on the respective working rolls, and respective upper and lower outer backup rolls of still larger diameter bear toward the nip on the respective inner backup rolls. Thus the bendability of the small-diameter working rolls is largely canceled out by the rigidity of the larger-diameter backup rolls so that the large forces required for rolling can be brought to bear on the workpiece.
In copending patent application No. 352,520 filed Feb. 26, 1982 a rolling stand is disclosed comprising a frame in which upper and lower working rolls are journaled for rotation about respective parallel upper and lower working-roll axes and define a workpiece nip. Respective upper and lower backup-roll guide elements vertically flank the working rolls and are each at least partially vertically displaceable relative to the frame. Respective upper and lower backup-roll journal blocks are axially displaceable but vertically fixed relative to the guide elements and define parallel upper and lower inner axes flanking the working axes. Respective inner backup rolls are journaled in the blocks for rotation about the inner axes and bear radially toward the nip on the working rolls. The inner backup rolls are therefore axially displaceable in the guide elements. A pair of outer backup rolls are journaled in the frame for rotation about outer axes coplanar with the respective-inner axes and bear radially toward the nip on the inner backup rolls. Means is provided including respective vertically effective actuators for exerting a force at least generally parallel to the planes between each journal block and the frame to bend the inner backup rolls and for displacing the force axially relative to the journal blocks.
In such arrangements it is necessary to change the working rolls and the inner pair of backup rolls periodically. These elements are normally of relatively small diameter and wear rather rapidly. Typically they are permanently mounted in their journal blocks, and once worn or scored are removed with their journal blocks and taken to a shop where the rolls are turned down. Obviously this machining is such a time-consuming process that a spare set of rolls is kept near the roll stand so they can be alternated in the stand with the other set.
Brazilian patent document No. 7,602,387 filed by Noriyoshi Sonobe with a claim to a Japanese priority date of Apr. 12, 1975 describes a roll-changing system for such an arrangement which has a changing carriage that can move both in a transverse direction extending horizontally perpendicular to the workpiece travel direction and parallel to the roll axes and a longitudinal direction extending horizontally parallel to the workpiece travel direction. This carriage has two adjacent holders for two sets of rolls, each holder being shaped to hold a full set of rolls in a stack, with the two working rolls vertically superposed and vertically flanked by two backup rolls and with the upper working and backup roll resting on the underlying rolls. Thus a full set of rolls, which here is intended to include two journal blocks for each roll, is held in the one holder, with the roll axes lying in a common vertical plane. In this system the journal blocks for the backup rolls must be smaller than those of the working rolls, measured longitudinally, to allow the above-described stacking.
To use such an arrangement the one holder is loaded up either with a full fresh set of two working and two backup rolls or with a set of working rolls only, as same wear much more rapidly than the backup rolls. The loaded carriage is then pulled up next to the stand whose rolls need replacement. A crane or the like takes the rolls to be replaced off the stand and stacks them in the empty holder, then takes the rolls from the full holder and installs them in the stand.
When the backup rolls are still fairly new it is standard to load the carriage only with a set of working rolls. If the backup rolls wear prematurely, this unreadiness can cause considerable down time while a fresh set of backup rolls is fetched from the shop. Once the backup rolls are old enough to possibly need replacement, the prudent operator keeps a full set of rolls ready for the change, and just replaces all four even if the backup rolls turn out to be reusable. Since the holder directly supports only the lower working and backup rolls, the upper working and backup rolls being supported on the lower ones, it is necessary to unstack the rolls in the holder starting from the top, although independent supporting of the lower working roll makes it possible to load the holder only with two working rolls, the upper of which will be supported on the lower.
German patent document No. 3,123,933 filed by T. Sekiya with a claim to a Japanese priority date of June 18, 1980 has a more complex system that does not put substantial dimension constraints on the journal blocks for the backup rolls, allowing them to be the same size as those of the working rolls. Nonetheless this system is set up so that if one plans to change certain rolls and it is necessary to change more or less, the downtime increases while the carriage is moved about and reloaded. Even when the rolls are pushed axially out of the roll stand into the empty holder and the fresh rolls are pushed axially oppositely back into the stand, this arrangement has little flexibility.